The throttle position sensor (TPS) is a critical component of any fuel injection system, all fuel injected Hondas come with them. A misadjusted TPS will cause a lot of problems, including those you describe.

Every part is "factory adjusted." Honda likes to attach them with headless screws, so drill those out and replace them with normal screws... your mechanic probably did this already in order to swap them. He also may have adjusted it to bad specs. From what you describe, it shouldn't be too far off. Use a multimeter to check it's resistance through the full throttle motion.

If the engine cuts fuel at the old H23A cut RPM, you should check to see if the H22A ECU has been installed.